ZF Transmission question - temps

[BenchTest]

I've observed a very repeatable trend and I'm curious if others have. This also may be a design build for this transmission? My fluid runs mid to upper 180s when ambient temps are below 60. As ambient temps increase, my fluid cools to low 170s. Is this an intentional temperature regulation to keep fluid thinned at lower temps for flow properties and fuel economy (thinner fluids are easier to move, less drag)?

 

[crash68]

With the ZF transmissions if the transmission temperature is staying at or below the coolant temperature it's working as intended. If the temperature is spiking really high over the coolant temp, the TMU on the side of the transmission will probably needs to be replaced.

 

[HEMIMANN]

With the ZF transmissions if the transmission temperature is staying at or below the coolant temperature it's working as intended. If the temperature is spiking really high over the coolant temp, the TMU on the side of the transmission will probably needs to be replaced.

Thermostat bypass kit?

 

[Wild one]

I've observed a very repeatable trend and I'm curious if others have. This also may be a design build for this transmission? My fluid runs mid to upper 180s when ambient temps are below 60. As ambient temps increase, my fluid cools to low 170s. Is this an intentional temperature regulation to keep fluid thinned at lower temps for flow properties and fuel economy (thinner fluids are easier to move, less drag)?

The 8 speeds use their own thermostat,it's in the TMU on the side of the transmission as Crash stated.They have been known to give trouble. For now i wouldn't worry to much about your's,but if the transmission starts to regulary run above 200F in the summer,you might want to look into either replacing the Thermal Management Unit on the side of the transmission,or pull the thermostat out and replace it with one of Caulk04's thermostat bypasses.The thermostat is a pellet style thermostat,similiar to the engine thermostat,so it doesn't really change opening temps in relation to ambient temps,as much as it does to fluid temps. Your's could be acting up a bit,but as long as the transmission temps don't sky rocket,i wouldn't worry to much about it yet,but you might want to keep an eye on the transmission temp from here on in.
How many miles are on your truck,ZF reconmends doing a transmission service on the 8 speed between 50,000 (if you tow alot) and 80,000 miles or 8 years which ever comes first

 

[BenchTest]

The 8 speeds use their own thermostat,it's in the TMU on the side of the transmission as Crash stated.They have been known to give trouble. For now i wouldn't worry to much about your's,but if the transmission starts to regulary run above 200F in the summer,you might want to look into either replacing the Thermal Management Unit on the side of the transmission,or pull the thermostat out and replace it with one of Caulk04's thermostat bypasses.The thermostat is a pellet style thermostat,similiar to the engine thermostat,so it doesn't really change opening temps in relation to ambient temps,as much as it does to fluid temps. Your's could be acting up a bit,but as long as the transmission temps don't sky rocket,i wouldn't worry to much about it yet,but you might want to keep an eye on the transmission temp from here on in.
How many miles are on your truck,ZF reconmends doing a transmission service on the 8 speed between 50,000 (if you tow alot) and 80,000 miles or 8 years which ever comes first

Pan/filter was replaced at 54k miles and I currently set at 65k. Was behaving in this manner prior to trans service. It's temperature swings have stayed the same prior/post trans service. I serviced the trans as a preventative at 54k, not due to any performance related issues.

 

[CanuckRam1313]

Highly recommend the @caulk04 transmission bypass cooler mod!
I've got one in my truck, in my step-daughters truck, and a third on order for an acquaintances truck, too.

Do a transmission fluid and filter change at the same time as well. I'm seeing trans temps decreases of up to 30deg with this mod.

My trans runs great now, and I will be doing a 60K to 70K oil & filter change interval moving forward. That reminds me.... I'm near due for another fluid and filter change....

 

[BenchTest]

Does the TMU exist on both variants (845RE & 8HP70)?

 

[caulk04]

Yes, all 8spd in 1500 Rams (not the TRX).

The Hemi powered Wagoneer and Grand Wagoneer as well.

 

[Wild one]

Pan/filter was replaced at 54k miles and I currently set at 65k. Was behaving in this manner prior to trans service. It's temperature swings have stayed the same prior/post trans service. I serviced the trans as a preventative at 54k, not due to any performance related issues.

Did you follow these directions,especially the part about leveling the pan rail.

 

[indept]

Highly recommend the @caulk04 transmission bypass cooler mod!
I've got one in my truck, in my step-daughters truck, and a third on order for an acquaintances truck, too.

Do a transmission fluid and filter change at the same time as well. I'm seeing trans temps decreases of up to 30deg with this mod.

My trans runs great now, and I will be doing a 60K to 70K oil & filter change interval moving forward. That reminds me.... I'm near due for another fluid and filter change....

Do you have a link?

 

[BenchTest]

Did you follow these directions,especially the part about leveling the pan rail.

Proper service procedures were followed. The transmission was level.

 

[CanuckRam1313]

Do you have a link?

Link?
@caulk04 is the man to contact in our community for his designed mod.

 

[caulk04]

I will hopefully have a distributor soon and in that case there will be a link to his store. In the meantime though, shoot me a direct message on here and we'll get one going.

@AEDELGOD

 

[MB 1]

Ditto on all the forgoing. Here's a link to RevMax for a bypass kit: https://revmaxconverters.com/produc...-8hp75-transmission-cooler-thermostat-bypass/
With this install, you'll have three options:
Option One: Install warmer blocking plate only. This will get rid of the immediate unneeded heating of the transmission fluid. This will cause the transmission to run about 20 degrees cooler all the time and not heat up so quickly.

Option Two: Remove thermostatic valve only. Remove the plastic end plug which is notorious for cracking and leaking. Install the new brass end plug and omit the factory thermostat. This option will cause the unit to heat up quickly but run at a slightly lower temperature.

Option Three (Most Common): Install the warmer blocking plate and brass endplug upgrade and remove the thermostat. This will eliminate the rapid heating from the warming unit and then by also removing the thermostat you can expect up to a 50-70 degree drop in operating temperature. You will also have a 87% increase in cooler low by using this option as the restrictive thermostat is now removed and the maximum amount of cooler flow is now flowing.

I used option three above and my temps are now running well more than 35 degrees lower than before. In addition, nearly all of the controlled airflow louvers behind the grill were removed, a new aluminum oil pan and filter were installed and the transmission flushed with fresh Valvoline MaxLife fluid. It all worked as advertised and better than expected.

 

[caulk04]

The revmax kit is fine, so long as you use it properly. 'option 3' is the only real safe option.

However, if you go HERE and pick up this thermal bypass you'll save money and time on install while accomplishing the exact same end goal.

 

[BossHogg]

Thermostat bypass kit?

Keep in mind the transmission's lubricating fluid has an optimal operating temperature range that offers the highest level of lubricity. You want to keep the operating temperature in that range.

 

[Wild one]

Ditto on all the forgoing. Here's a link to RevMax for a bypass kit: https://revmaxconverters.com/produc...-8hp75-transmission-cooler-thermostat-bypass/
With this install, you'll have three options:
Option One: Install warmer blocking plate only. This will get rid of the immediate unneeded heating of the transmission fluid. This will cause the transmission to run about 20 degrees cooler all the time and not heat up so quickly.

Option Two: Remove thermostatic valve only. Remove the plastic end plug which is notorious for cracking and leaking. Install the new brass end plug and omit the factory thermostat. This option will cause the unit to heat up quickly but run at a slightly lower temperature.

Option Three (Most Common): Install the warmer blocking plate and brass endplug upgrade and remove the thermostat. This will eliminate the rapid heating from the warming unit and then by also removing the thermostat you can expect up to a 50-70 degree drop in operating temperature. You will also have a 87% increase in cooler low by using this option as the restrictive thermostat is now removed and the maximum amount of cooler flow is now flowing.

I used option three above and my temps are now running well more than 35 degrees lower than before. In addition, nearly all of the controlled airflow louvers behind the grill were removed, a new aluminum oil pan and filter were installed and the transmission flushed with fresh Valvoline MaxLife fluid. It all worked as advertised and better than expected.

Option 1 and 2 will cook your 8 speed. Both CrazyKid and i pointed that out to Revmax a couple years ago,and why they still have it on their site is beyond me. Caulk04's bypass is the superior option,way easier to install then the revmax kit.

 

[Wild one]

Keep in mind the transmission's lubricating fluid has an optimal operating temperature range that offers the highest level of lubricity. You want to keep the operating temperature in that range.

What is that operating temperature range? The 8 speeds in the HD's run at 160/165 unloaded and usually stay under 170 while towing in excess of 7,000lbs,back road summer evening cruising at 45/50 mph the 8 speed in my wifes 6.4 Challenger with a factory high stall convertor runs at 150/155F,so just what is the optimal temp??.
You check the fluid level at no more then 122F,so is that optimal temp?

 

[HEMIMANN]

Tribologists generally see 140F as an optimal oil temperature in circulating oil systems - not too hot to promote rapid oxidation, yet hot enough to reduce viscous shear drag and pumping losses.

From when I worked for Mobil Oil as a Lubrication Engineer. I don't want an oil heater in winter for my transmission - too unreliable. And in Ram's case, flow restrictive, too, so when it's hot outside, the oil gets too hot and starts oxidizing faster. Yes, synthetics oxidize too, at a slower rate than mineral oils. Oxidation is exponentially faster with rising temperature above 140F bulk sump temp.

Keep in mind that bulk oil sump temp is not the hottest temp the oil sees - it is hotter than 140F when shearing through the torque converter vanes, the gear teeth, and the clutch discs. I don't give a rip about cooler than ideal oil temp in saving tenths of a mile per gear at the expensive of the life of my transmission.

 

[BossHogg]

What is that operating temperature range? The 8 speeds in the HD's run at 160/165 unloaded and usually stay under 170 while towing in excess of 7,000lbs,back road summer evening cruising at 45/50 mph the 8 speed in my wifes 6.4 Challenger with a factory high stall convertor runs at 150/155F,so just what is the optimal temp??.
You check the fluid level at no more then 122F,so is that optimal temp?

It would be best to get the optimal operating temperature range of the transmission fluid from the manufacturer. My point was simply to be aware of the optimal temperature range.

I didn't know you could check the fluid level of the ZF, how is that done?